The present invention relates to glazing provided with thin-film multilayer coatings that act on solar radiation, especially glazing intended for thermal insulation and/or solar protection.
The invention also relates to this type of glazing once opacified so as to form part of a building wall cladding panel, called “curtain walling”, which makes it possible, in combination with window glazing, to provide external surfaces of buildings entirely made from glass.
This type of glazing has been used for many years in the building sector, on the one hand to improve the thermal insulation of buildings and, on the other hand, to limit the amount of solar radiation penetrating the building (i.e. to limit the greenhouse effect). The radiation of interest, then, is solar radiation comprising the light spectrum extending from UV rays (wavelength equal to about 290 nm) to the near infrared (wavelength equal to about 2500 nm) and to thermal infrared radiation (with a wavelength of between about 2500 nm and 50 microns).
A first solution consists in varying the composition of the glass so as to obtain the desired characteristics. However, this solution proves to be neither practical nor economic, since to modify the glass composition it is necessary beforehand to empty the glass manufacturing furnace, which is expensive and takes a great deal of time. It is therefore preferable to use the solution consisting in depositing one or more thin films on at least one of the faces of the glass. In a multilayer coating, at least two different types of layers may be distinguished: functional layers, which give the multilayer coating essentially all of its thermal properties, and protection layers, generally made of transparent dielectric materials, the main role of which is that of providing the functional layers with chemical and/or mechanical protection.
However, certain uses of the glass require particular grades of this material. Thus, in the architectural and automotive fields, it is desirable or even necessary to use toughened glass (“safety” glass), the toughening or toughening process giving the glass good mechanical strength. Unfortunately, the toughened glass cannot be cut and it is therefore necessary for the glass to have its final shape and dimensions before the toughening or toughening process. Since the toughening of the glass is carried out by heating the glass to a high temperature (close to 700° C.) and then rapidly lowering the temperature (thereby creating mechanical stresses within the glass), thin layers deposited on the glass before the toughening or toughening process generally cannot withstand such a treatment and lose their optical and/or thermal properties. Moreover, the solution consisting in depositing thin films on the already toughened glass poses logistic problems and is not industrially viable.
Another property often required of the glass is to be able to withstand a heat treatment so as to be worked, in order to give it a curved or bent shape—the glass is then referred to as being “bendable”.
One technical problem to be solved is therefore that of developing a thin-film multilayer coating whose properties are not degraded when the glass on which it has been deposited is toughened and/or bent. In other words, the thin-film multilayer coating must be “toughenable” and “bendable”. The properties of the thin films that must not be degraded are in particular the solar radiation filtration performance and the optical characteristics, such as colors and light transmission intensity.
Solutions have already been proposed in the form of relatively simple multilayer coatings. Thus, an example of architectural solar-protection glazing is given in patents EP 0 511 901 and EP 0 678 483: this involves functional layers, for solar radiation filtration, layers made of a nickel-chromium alloy, optionally nitrided, or made of stainless steel or made of tantalum, and these are placed between two layers of dielectric made of a metal oxide, such as SnO2, TiO2 or Ta2O5. However, such glazing is not truly “bendable” or “toughenable” since the oxide layers surrounding the functional layer cannot prevent its oxidation during bending or toughening, oxidation being accompanied by a modification of the light transmission and the appearance of the glazing in its entirety.
More recently, patent application WO 01/21540 A1 has proposed a transparent substrate provided with a thin-film multilayer coating consisting of a functional layer made of metal (Nb, Ta, Zr) or made of a nitride of this metal, and an overlayer made of aluminum nitride or oxynitride and/or silicon nitride or oxynitride. This solution is relatively satisfactory since the multilayer coating is “bendable”, “toughenable” and mechanically strong, and has good optical characteristics. However, if it is desired to reduce the light transmission TL, it is necessary to increase the thickness of the functional layer, this having the drawback of increasing the light reflections, in particular inside the building. When it is dark outside (or at night), there is a tendency, inside the building, to now see only the thin-film multilayer coating, the glazing then taking on a relatively intense, and unattractive, color, dominant in the yellow/orange. In the CIE Lab model of color representation developed by the CIE (International Illumination Commission), these colors correspond to a* greater than 0 and b* very much greater than 0. The ideal in this model is to obtain values close to zero for the components a* and b*, resulting in less vivid colors, tending toward shades of gray (more neutral colors), and therefore more pleasant.